450 CHARLES EMERSON PERT 



and Lonely Lake. Probably Ballston Lake is thus situated. (See 



Fig- I3-) 



Under several of these gravel plateaus, over wide areas, clay is 

 reported. In the bottom of the Round Lake depression there is 

 till, and a limited coarse gravel area with deep sinks in it, although 

 clay and stratified drift rise in steep faces to the north and to the 

 west, and perhaps in other directions. It is believed that these 

 northeast-southwest depressions were occupied by masses of stagnant 

 ice while subsequent plateaus to the northwest were being built, and 

 that the northeast-southwest trend of the depressions indicate some- 

 thing of the direction of the ice-edge as it retreated. At Glens Falls ^ 

 and north a succession of gravel plateaus is believed to mark the 

 successive positions of the ice-edge in a similar way, but they are 

 not separated by wide depressions, or depressions of any kind so gen- 

 erally. Below the level of these gravel plateaus are secondary deltas 

 derived from higher gravels by erosion. It is believed that they 

 have been recognized at South Bethlehem (two levels — one on 

 Sprayt Kill and one on the Oniskethau) (Fig. 13, No. 62), on the 

 Hoosick River (Fig. 13, No. 90), on the Batten Kill near Schuyler- 

 ville (Fig, 13, No. 91), and on the Hudson in the vicinity of Glens 

 Falls (two levels) (Fig. 18, Nos. 94 and 86.) 



Elevations above old lake- or old sea-floor. — Above the plain in 

 situations not confined to its borders there rises another class of eleva- 

 tions, some of which were islands in the sea or lake, when the gravel 

 plateaus and deltas were being made. These hills sometimes are drift 

 hills. More often they are drift-covered rock hills. Such islands 

 may be seen in the following places:^ (i) hill northeast of Saratoga; 

 (2) highland east of Saratoga Lake; (3) hills north and south of 

 Mohawk River; (4) hills southeast of Albany; (5) hills south of New 

 Baltimore and at numerous places southward, where the elevations 

 are ridges elongate in a north- south direction. Some of these hills 

 may have formed shallows only, at the highest stage of the Hudson 

 water body, but most of them were distinct islands and served to 

 break the water body up into several more or less separate portions. 

 There were doubtless other shallows or islands, and the elevations 



1 See also Warren Upham, American Gsologist, Vol. XXXII (1903), pp. 223-3o_ 



2 For these elevations see Fig. 13. 



